What is the best training to prepare for a Tough Mudder or Spartan Race?

Take the registration form, light it on fire, sit back and drink a cold beer instead. I have never figured out why people voluntarily run and pay money to do it.

My 13 year old grandson.

My wife and I trained for a tough mudder. We started with a 2 mile run stopping every half mile to do ten reps of one of the following Jumping jacks, push ups, sit ups, burpees and lunges. We worked our way up to ten mile runs stopping every half mile to do 30 reps of one of the above. It worked well however, I would add pull ups into the end of the work out if I did it again.